Flashpoint is the lowest temperature at which a liquid produces sufficient vapor to form an ignitable mixture with air near its surface. At the flashpoint, the vapor concentration reaches the lower flammable limit (LFL), meaning that an ignition source can cause a brief flash of flame. Sustained combustion requires a somewhat higher temperature — the fire point — but flashpoint is the standard property used for hazard classification and regulatory compliance.
Flashpoint is the primary parameter used to classify liquids as flammable or combustible under OSHA, NFPA 30, and DOT regulations, and it drives hazardous area classification decisions under IEC 60079-10-1 and NFPA 497. A lower flashpoint means a liquid produces ignitable vapors at lower ambient temperatures, creating a more persistent vapor source in the surrounding area. Different regulatory bodies apply different threshold values, so the same liquid may be classified as flammable under one standard and combustible under another.
Key Points
- Flashpoint is measured using standardized test methods — open cup (ASTM D92) or closed cup (ASTM D93, ASTM D56); closed-cup values are slightly lower and are used in most regulatory definitions.
- There are various definitions for flammable liquids in various standards and countries and they can be confusing. For example, OSHA 29 CFR 1910.106 and NFPA 30 define flammable liquids as those with a flashpoint below 100°F (37.8°C); the GHS/HazCom 2012 system and DOT use 60°C (140°F) as the upper threshold.
- Liquids stored or processed above their flashpoint are treated as active vapor sources for zone classification purposes under IEC 60079-10-1, requiring appropriately rated electrical equipment in the surrounding area.
Example
Gasoline has a flashpoint of approximately −43°C, meaning it produces ignitable vapors well below freezing. A gasoline transfer pump operating outdoors in winter still generates a hazardous zone even when ambient temperatures are far below 0°C — a practical illustration of why flashpoint, not ambient temperature, drives zone classification decisions.
See Also: flammable liquid, flammable gas, hazardous areas, NFPA hazard ratings
Cited Sources
- ASTM D56, D93 — Standard Test Methods for Flash Point
- NFPA 30, Flammable and Combustible Liquids Code
- OSHA 29 CFR 1910.106 — Flammable Liquids
- IEC 60079-10-1, Explosive Atmospheres — Classification of Areas: Flammable Gas Atmospheres